Preoperative Management of Hypothyroidism for Surgical Clearance
Direct Recommendation
Continue levothyroxine without interruption through the morning of surgery, including the day of the procedure, and delay elective surgery until biochemical euthyroidism (TSH 0.5–2.0 mIU/L) is achieved whenever feasible. 1
Medication Management on Day of Surgery
Do not hold levothyroxine perioperatively. The American College of Cardiology explicitly recommends continuing levothyroxine on the morning of surgery without interruption to prevent perioperative complications and avoid destabilizing thyroid status. 1
No stress-dose adjustment is required for levothyroxine, unlike glucocorticoids, as it does not increase bleeding risk or interfere with anesthesia. 1
Administer levothyroxine as a single dose on an empty stomach, one-half to one hour before the procedure if possible, with a full glass of water. 1
Target Thyroid Function Tests Before Elective Surgery
Delay elective surgery until euthyroidism is achieved whenever feasible to reduce perioperative risks, particularly cardiovascular complications. 1, 2
Target TSH range: 0.5–2.0 mIU/L (normal physiologic range) for patients with hypothyroidism undergoing surgery for benign indications. 3
Measure serum TSH as part of the preoperative evaluation to document euthyroidism before proceeding with elective surgery. 2
Even subclinical hypothyroidism (TSH 4.5–10 mIU/L) increases perioperative risks, particularly cardiovascular complications, so optimization is recommended. 1
Levothyroxine Dosing Strategy
Standard initial dosing: 1.5–1.6 μg/kg actual body weight for patients starting levothyroxine replacement, with TSH-guided adjustments at 6 weeks. 3
Lower starting doses (25–50 μg) are appropriate for elderly patients, those with residual thyroid function, low body weight, or significant cardiac comorbidities. 4
Recheck TSH every 6 weeks after each dose adjustment until the target TSH of 0.5–2.0 mIU/L is achieved. 3
Availability of intermediate tablet strengths (e.g., 37.5 μg, 62.5 μg) facilitates precise dose titration in the 25–75 μg range and supports adherence to single-tablet daily regimens. 4
Timing Before Elective Surgery
Allow at least 6 weeks after initiating or adjusting levothyroxine before elective surgery to permit thyroid hormone levels to reach steady state and confirm biochemical euthyroidism. 3
Detection of hypothyroidism as close to 28 days before surgery provides sufficient time for evaluation and management, though this recommendation comes from anemia guidelines and should be adapted to thyroid optimization timelines. 5
Urgent or Emergent Surgery in Uncontrolled Hypothyroidism
For urgent surgery when euthyroidism cannot be achieved: proceed with surgery after cardiovascular stabilization and close perioperative monitoring, as delaying surgery may pose greater risk than operating in the hypothyroid state. 2
One exception to preoperative thyroid hormone therapy: patients with angina or coronary artery disease requiring bypass grafting, angioplasty, or stenting should have coronary blood flow addressed first, with thyroid hormone therapy initiated afterwards to avoid taxing the ischemic myocardium. 2
Subcutaneous or intravenous levothyroxine can be used in cases of malabsorption or inability to take oral medication, though this is rarely needed in the preoperative setting. 6
Critical Preoperative Assessment
Rule out adrenal insufficiency before initiating or continuing levothyroxine therapy, as hypothyroidism treatment is contraindicated until adrenal insufficiency is corrected. 1
Avoid etomidate for induction when possible, as it suppresses cortisol production, and maintain high clinical suspicion for relative adrenal insufficiency throughout the perioperative period. 1
Monitor for signs of severe hypothyroidism: lethargy, prolonged ventilation requirements, hypotension, gastrointestinal complications, and neuropsychiatric complications, particularly in patients with coronary artery disease. 1
Postoperative Management
Resume oral levothyroxine as soon as the patient can tolerate oral intake postoperatively, administered as a single dose on an empty stomach. 1
Continue monitoring for complications of severe hypothyroidism in the immediate postoperative period, including cardiovascular instability and delayed recovery. 1
Common Pitfalls to Avoid
Do not hold levothyroxine perioperatively, as interruption destabilizes thyroid status and worsens surgical outcomes. 1
Do not overlook subclinical hypothyroidism (TSH 4.5–10 mIU/L), as even mild thyroid dysfunction increases perioperative cardiovascular risks. 1
Do not confuse hypothyroidism with euthyroid sick syndrome in critically ill or surgical patients, as low serum thyroid hormones in nonthyroidal illness do not warrant thyroid hormone replacement and may be harmful. 2
Do not initiate aggressive levothyroxine therapy in patients with untreated coronary artery disease without first addressing coronary blood flow. 2